The present invention relates to an electron beam lithography apparatus and a method thereof, and more particularly to an electron beam lithography apparatus for drawing a desired pattern on a specimen by irradiating the electron beam thereon and a method thereof.
A fine processing technique in which an electron gun generates electron beams to irradiate a specimen, thereby conducting a fine processing so as to draw a desired pattern thereon, is widely practiced. In particular, such a fine processing technique is extensively utilized in manufacture of master pattern drawings of semiconductor designs. In order to draw a desired pattern, it is necessary to be able to direct an electron beam to an arbitrary position on a specimen for exposure thereof. A deflector serves this purpose and deflects the electron beam. The deflector is formed, for example, by a coil or the like, and generates a magnetic field. In accordance with changes in a voltage applied to the deflector, the electron beam is deflected so as to draw a desired pattern. When the pattern to be drawn exceeds the range of allowable deflection, the specimen itself is moved by transferring a specimen stage carrying the specimen. These related prior arts are disclosed in the Japanese Patent Application Laid-Open No.2-138723(1990) and so on.
However, even when a voltage for controlling the deflector is changed to change the deflection of the electron beam, the deflector is not changed, instantly. Namely, the voltage increases along a predetermined Gradient, and further undergoes a hunting phenomenon until the voltage is stabilized. If the voltage in the deflector is not stabilized, a deflection quantity of the electron bean cannot be determined, thereby causing the position of the electron beam to drift. According to the prior art, to solve this problem an exposure of an electron beam on the specimen is blocked by a beam blanker until the voltage in the deflector is sufficiently stabilized.
Further, once the specimen stage is moved, the stage undergoes an oscillation, taking some time until it stabilizes. If the stage does not stabilize, the electron beam cannot pinpoint an accurate position relative to the specimen. Thereby, according to the prior art, the electron beam was blocked from reaching the specimen until the stage had been stabilized.
Lately, very complicated drawing patterns are required, and such demand is increasing, in particular, in the fields of large scale integrated circuits (LSIs) and so on. For example, in manufacture of 64M RAMs, it is necessary to repeat an electron beam exposure as many as something on the order of 10.sup.10 times. Thereby, a high speed pattern drawing is desired to be implemented. The time required for drawing a pattern depends mainly on the exposure time of the electron beam and also on the time during which the electron beam is interrupted. According to the prior art, although the electron beam was blocked by the blanker until the voltage in the deflector had stabilized, if this interruption time can be reduced, a high speed pattern drawing can be attained. However, when the time for interruption of the electron beam is too short, the electron beam drifts, thereby making it difficult to execute a precise pattern drawing.
Further, the time elapsed until the completion of pattern drawing depends also on an electron beam interruption time required for moving the specimen stage. Although the electron beam was blocked until the stage had stabilized completely according to the prior art, if this blocking time is reduced, a high speed drawing can be attained. However, when the electron beam interruption time is shortened, the electron beam is allowed to be irradiated while the stage is still in drift, thereby making it difficult to perform a precise drawing.